A team has used CRISPR to make a record-breaking 13,200 changes to the DNA of a single human cell. The feat takes us a step closer聽to being able to thoroughly rewrite the genomes of our cells and other organisms.
Half of our genomes 鈥� the complete set of DNA inside our cells 鈥� consist of hundreds of thousands of copies of genetic parasites called transposons. These transposons code for genes that copy and paste themselves from one location in the genome to another. Most copies of these transposons are so full of mutations that they no longer work, but many remain active and can cause聽cancers and other disorders if they paste themselves into the wrong spot.
George Church聽at Harvard University and his colleagues decided to use CRISPR genome editing to deactivate a transposon called LINE-1. They first tried using the standard form of CRISPR, which involves cutting DNA. But cutting DNA in hundreds of sites killed the cells, the team found.
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So the team turned to a newer form of CRISPR called base editing. This transforms one DNA letter to another without making any cuts. Using this technique, they managed to edit 50 per cent of the 26,000 active LINE-1 transposons in a human cell.聽鈥淲e hope, in the future, to knock-out 100 per cent of active LINE elements,鈥� says Church.
Although the team know they successfully made 13,200 edits, they have not been able to assess how many unwanted, extra mutations were introduced by this process. This is extremely difficult to figure out because LINE sequences are so repetitive.
Church鈥檚 team set the previous record for the most edits at once when they disabled the 62 copies of a virus lurking in the genome of pig cells.
Both these feats involved making the same change to numerous copies of the same sequence in the genome of cells. Next, Church wants to try to make 4000 different changes to 4000 different sequences in human cells, with the aim of freeing up one of the standard three-letter codes in our DNA for other uses. The published record so far is 30, he says.
If it works, this approach may also make it possible to edit the genomes of living animals such as elephants to make them more like extinct ones such as mammoths.
bioRxiv
